Montgomery
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Montgomery clear sky chart from 2005-11-06 to 2024-11-25.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	16% 7% 2 6% 4 5% 4 4 6% 7% 38%	101538
	Night	17% 7% 2 6% 4 4 4 3 5% 7% 40%	97936
Transparency	Day	44% 5% 12% 24% 14% 2	105057
	Night	43% 5% 12% 24% 15% 2	102506
Seeing	Day	21% 14% 28% 23% 11% 3	14975
	Night	20% 12% 29% 29% 10% 1	24109

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	14% 8% 2 5% 4 3 5% 4 5% 6% 44%	2517
	11th to 20th	Day	14% 8% 4 10% 7% 5% 5% 4 6% 5% 33%	2520
	21st to end	Day	20% 13% 4 8% 4 4 3 3 5% 5% 31%	2978
February	1st to 10th	Day	15% 10% 2 8% 5% 5% 6% 4 5% 7% 33%	1710
	11th to 20th	Day	14% 7% 3 7% 5% 5% 4 3 5% 6% 40%	1828
	21st to end	Day	18% 9% 3 5% 5% 4 4 4 5% 6% 37%	1570
March	1st to 10th	Day	25% 9% 3 7% 5% 4 3 3 4 5% 34%	3116
	11th to 20th	Day	10% 7% 2 7% 5% 5% 4 4 6% 8% 41%	3347
	21st to end	Day	21% 7% 2 5% 5% 4 4 3 4 6% 39%	4124
April	1st to 10th	Day	18% 8% 3 6% 4 4 5% 4 5% 6% 37%	2280
	11th to 20th	Day	17% 7% 3 7% 5% 4 4 3 5% 6% 40%	2254
	21st to end	Day	19% 7% 3 7% 4 4 5% 3 5% 5% 38%	2311
May	1st to 10th	Day	25% 8% 2 6% 4 4 4 3 5% 7% 31%	4156
	11th to 20th	Day	20% 8% 2 7% 5% 5% 5% 3 6% 6% 32%	4398
	21st to end	Day	12% 5% 2 5% 4 4 4 5% 7% 10% 42%	4837
June	1st to 10th	Day	16% 5% 1 6% 5% 5% 6% 4 7% 10% 35%	2660
	11th to 20th	Day	14% 6% 2 6% 5% 5% 5% 5% 7% 9% 36%	2660
	21st to end	Day	13% 6% 3 7% 5% 5% 5% 4 7% 8% 38%	2660
July	1st to 10th	Day	9% 7% 3 7% 6% 6% 6% 5% 8% 9% 35%	4440
	11th to 20th	Day	10% 6% 2 6% 5% 6% 5% 5% 7% 11% 38%	4440
	21st to end	Day	13% 8% 3 7% 5% 5% 5% 5% 6% 8% 34%	4814
August	1st to 10th	Day	20% 6% 2 6% 4 6% 4 4 6% 7% 33%	4249
	11th to 20th	Day	12% 7% 2 6% 4 4 5% 4 7% 9% 39%	3730
	21st to end	Day	13% 5% 2 5% 4 3 5% 4 6% 10% 44%	4180
September	1st to 10th	Day	14% 7% 3 5% 4 5% 4 3 5% 7% 43%	2280
	11th to 20th	Day	13% 5% 1 5% 3 4 4 3 5% 7% 50%	2209
	21st to end	Day	17% 6% 2 6% 5% 4 4 3 6% 6% 41%	2090
October	1st to 10th	Day	20% 6% 2 6% 4 4 4 3 5% 6% 41%	1966
	11th to 20th	Day	14% 6% 2 6% 3 5% 5% 3 6% 8% 43%	1900
	21st to end	Day	21% 7% 2 6% 4 4 5% 4 5% 6% 36%	1933
November	1st to 10th	Day	13% 6% 2 5% 4 4 3 2 4 6% 51%	1761
	11th to 20th	Day	16% 7% 3 5% 3 4 4 3 5% 7% 44%	1800
	21st to end	Day	16% 8% 3 5% 5% 4 3 4 5% 6% 40%	1622
December	1st to 10th	Day	19% 8% 3 7% 4 5% 5% 4 6% 6% 34%	1520
	11th to 20th	Day	22% 6% 2 4 3 3 4 3 5% 5% 41%	1906
	21st to end	Day	19% 10% 3 9% 5% 6% 4 5% 6% 6% 28%	2772
January	1st to 10th	Night	16% 7% 2 6% 4 4 4 3 5% 6% 43%	4429
	11th to 20th	Night	14% 8% 4 9% 5% 5% 4 4 4 5% 37%	4440
	21st to end	Night	23% 12% 2 6% 4 4 4 3 5% 6% 31%	4662
February	1st to 10th	Night	15% 10% 2 6% 4 4 5% 3 5% 6% 40%	2470
	11th to 20th	Night	14% 8% 3 7% 5% 4 5% 4 6% 5% 39%	2237
	21st to end	Night	18% 8% 2 7% 5% 4 4 3 4 5% 41%	1884
March	1st to 10th	Night	23% 9% 3 6% 4 4 3 3 5% 6% 35%	3724
	11th to 20th	Night	12% 8% 2 6% 5% 4 5% 3 7% 7% 41%	3607
	21st to end	Night	17% 9% 3 7% 5% 4 5% 2 4 5% 40%	3507
April	1st to 10th	Night	19% 7% 2 7% 5% 5% 5% 4 5% 6% 35%	1900
	11th to 20th	Night	19% 6% 2 6% 4 4 3 3 5% 7% 39%	1875
	21st to end	Night	20% 7% 3 6% 3 4 3 3 5% 6% 40%	1867
May	1st to 10th	Night	27% 8% 3 6% 3 4 4 4 5% 7% 31%	2812
	11th to 20th	Night	22% 9% 3 8% 4 4 4 3 5% 6% 33%	2495
	21st to end	Night	12% 7% 3 6% 3 5% 4 4 6% 8% 42%	2738
June	1st to 10th	Night	15% 6% 2 6% 4 4 5% 4 5% 8% 42%	1520
	11th to 20th	Night	13% 7% 2 5% 4 5% 4 4 6% 10% 41%	1520
	21st to end	Night	11% 5% 2 5% 3 4 4 4 7% 9% 45%	1520
July	1st to 10th	Night	10% 6% 2 6% 5% 5% 6% 4 7% 10% 38%	2520
	11th to 20th	Night	12% 5% 2 7% 5% 5% 5% 4 6% 10% 39%	2520
	21st to end	Night	15% 7% 2 7% 4 5% 4 5% 6% 8% 37%	2739
August	1st to 10th	Night	20% 6% 2 7% 4 5% 5% 4 6% 7% 34%	2652
	11th to 20th	Night	14% 7% 3 7% 5% 4 5% 3 5% 6% 41%	3089
	21st to end	Night	11% 5% 2 5% 4 4 4 4 5% 8% 50%	3476
September	1st to 10th	Night	14% 7% 2 5% 4 3 3 3 5% 7% 46%	1900
	11th to 20th	Night	14% 5% 1 4 3 4 3 3 4 7% 53%	1971
	21st to end	Night	17% 6% 2 5% 3 3 3 3 5% 6% 45%	2090
October	1st to 10th	Night	20% 7% 2 6% 4 4 4 3 4 6% 41%	2212
	11th to 20th	Night	15% 6% 2 6% 4 4 3 3 4 6% 48%	2280
	21st to end	Night	22% 7% 2 5% 4 3 4 4 5% 6% 40%	2663
November	1st to 10th	Night	12% 6% 2 6% 4 4 4 3 5% 6% 48%	2537
	11th to 20th	Night	18% 7% 2 4 4 3 4 3 5% 6% 44%	2600
	21st to end	Night	16% 6% 2 5% 4 4 4 4 5% 6% 43%	2648
December	1st to 10th	Night	19% 8% 3 5% 4 3 4 3 5% 7% 37%	2660
	11th to 20th	Night	20% 8% 3 5% 4 3 4 4 5% 6% 37%	3288
	21st to end	Night	22% 10% 3 7% 4 3 4 3 5% 5% 34%	4884

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	40% 4 11% 34% 10% 2	2518
	11th to 20th	Day	51% 4 11% 23% 10% 2	2520
	21st to end	Day	56% 3 10% 21% 9% 1	2978
February	1st to 10th	Day	49% 4 12% 21% 14% 1	1710
	11th to 20th	Day	45% 4 9% 23% 16% 3	1837
	21st to end	Day	48% 4 11% 22% 13% 2	1570
March	1st to 10th	Day	54% 3 10% 21% 9% 2	3119
	11th to 20th	Day	39% 5% 12% 31% 11% 1	3347
	21st to end	Day	47% 4 6% 16% 22% 5%	4124
April	1st to 10th	Day	48% 5% 9% 21% 14% 4	2280
	11th to 20th	Day	45% 4 11% 21% 16% 3	2254
	21st to end	Day	47% 5% 9% 21% 15% 4	2311
May	1st to 10th	Day	53% 4 12% 16% 13% 1	4170
	11th to 20th	Day	53% 4 13% 20% 9% 1	4402
	21st to end	Day	35% 6% 13% 28% 17% 2	4837
June	1st to 10th	Day	43% 6% 13% 22% 14% 1	2660
	11th to 20th	Day	42% 6% 14% 25% 11% 2	2660
	21st to end	Day	41% 7% 12% 26% 14% 1	2660
July	1st to 10th	Day	43% 7% 12% 21% 15% 1	4370
	11th to 20th	Day	39% 6% 16% 25% 13% 1	4365
	21st to end	Day	47% 6% 12% 19% 15% 2	4661
August	1st to 10th	Day	49% 5% 13% 22% 10% 1	4235
	11th to 20th	Day	39% 6% 16% 28% 10%	3766
	21st to end	Day	36% 5% 11% 31% 15% 1	4180
September	1st to 10th	Day	40% 5% 11% 24% 17% 2	2280
	11th to 20th	Day	34% 4 9% 27% 24% 2	2209
	21st to end	Day	43% 5% 11% 22% 17% 3	2090
October	1st to 10th	Day	41% 5% 8% 20% 23% 3	3265
	11th to 20th	Day	31% 4 9% 29% 24% 3	3140
	21st to end	Day	31% 4 15% 27% 19% 4	3158
November	1st to 10th	Day	36% 4 12% 27% 19% 3	1761
	11th to 20th	Day	41% 3 11% 24% 19% 3	1800
	21st to end	Day	44% 4 14% 27% 10% 2	1622
December	1st to 10th	Day	50% 4 14% 19% 13%	1520
	11th to 20th	Day	45% 3 16% 23% 11% 2	1906
	21st to end	Day	55% 5% 11% 21% 7%	2772
January	1st to 10th	Night	42% 4 11% 27% 12% 3	4429
	11th to 20th	Night	47% 6% 11% 23% 11% 2	4440
	21st to end	Night	53% 4 9% 22% 10% 1	4662
February	1st to 10th	Night	46% 5% 13% 22% 12% 1	2470
	11th to 20th	Night	45% 4 10% 19% 17% 4	2239
	21st to end	Night	46% 3 8% 24% 15% 4	1884
March	1st to 10th	Night	52% 4 11% 20% 11% 2	3734
	11th to 20th	Night	40% 5% 13% 26% 13% 2	3608
	21st to end	Night	47% 4 6% 15% 22% 5%	3507
April	1st to 10th	Night	50% 4 9% 20% 14% 3	1900
	11th to 20th	Night	45% 5% 9% 20% 19% 1	1875
	21st to end	Night	45% 4 8% 23% 16% 4	1867
May	1st to 10th	Night	53% 5% 10% 19% 11% 1	2818
	11th to 20th	Night	53% 4 13% 17% 11% 1	2496
	21st to end	Night	39% 6% 15% 26% 12% 2	2739
June	1st to 10th	Night	40% 6% 11% 24% 18% 1	1520
	11th to 20th	Night	39% 7% 15% 28% 10% 1	1520
	21st to end	Night	35% 7% 15% 27% 15% 1	1520
July	1st to 10th	Night	39% 8% 16% 21% 15% 2	2480
	11th to 20th	Night	41% 6% 13% 26% 13% 1	2472
	21st to end	Night	43% 6% 14% 17% 17% 2	2651
August	1st to 10th	Night	49% 7% 15% 18% 9% 1	2642
	11th to 20th	Night	43% 6% 14% 27% 9%	3119
	21st to end	Night	33% 5% 11% 34% 16% 1	3476
September	1st to 10th	Night	39% 6% 10% 27% 18% 1	1900
	11th to 20th	Night	33% 3 11% 26% 25% 2	1971
	21st to end	Night	40% 5% 9% 23% 22% 1	2090
October	1st to 10th	Night	42% 5% 10% 22% 19% 1	3693
	11th to 20th	Night	28% 3 9% 31% 26% 3	3779
	21st to end	Night	34% 4 13% 31% 18% 1	4388
November	1st to 10th	Night	38% 3 12% 24% 21% 3	2537
	11th to 20th	Night	42% 3 9% 24% 18% 4	2600
	21st to end	Night	41% 3 14% 30% 11% 1	2648
December	1st to 10th	Night	47% 4 12% 24% 13% 1	2660
	11th to 20th	Night	47% 5% 13% 19% 14% 3	3288
	21st to end	Night	52% 4 12% 22% 9%	4884

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	27% 21% 29% 19% 4	180
	11th to 20th	Day	33% 23% 30% 10% 4 1	180
	21st to end	Day	22% 23% 32% 17% 4 2	258
February	1st to 10th	Day	33% 22% 31% 11% 2	270
	11th to 20th	Day	25% 24% 35% 14% 2	436
	21st to end	Day	30% 20% 30% 15% 4	382
March	1st to 10th	Day	25% 20% 32% 18% 5%	460
	11th to 20th	Day	24% 25% 28% 18% 3 1	460
	21st to end	Day	31% 18% 28% 17% 5% 2	506
April	1st to 10th	Day	31% 20% 25% 16% 7% 2	460
	11th to 20th	Day	25% 25% 28% 12% 8% 2	452
	21st to end	Day	29% 18% 27% 18% 7% 2	460
May	1st to 10th	Day	34% 14% 26% 17% 7% 2	463
	11th to 20th	Day	20% 15% 34% 20% 9% 2	487
	21st to end	Day	19% 9% 27% 27% 15% 3	529
June	1st to 10th	Day	19% 11% 28% 25% 13% 2	490
	11th to 20th	Day	16% 12% 28% 30% 13% 2	490
	21st to end	Day	16% 13% 27% 29% 12% 3	490
July	1st to 10th	Day	14% 8% 26% 30% 17% 5%	485
	11th to 20th	Day	13% 4 27% 33% 18% 6%	484
	21st to end	Day	12% 7% 30% 34% 14% 3	532
August	1st to 10th	Day	12% 7% 25% 31% 17% 7%	486
	11th to 20th	Day	14% 7% 24% 31% 18% 6%	479
	21st to end	Day	12% 10% 24% 28% 17% 8%	539
September	1st to 10th	Day	18% 10% 22% 23% 17% 9%	490
	11th to 20th	Day	14% 8% 25% 22% 18% 13%	490
	21st to end	Day	21% 10% 26% 26% 13% 5%	490
October	1st to 10th	Day	27% 11% 20% 23% 14% 6%	490
	11th to 20th	Day	16% 15% 28% 25% 13% 3	490
	21st to end	Day	25% 12% 30% 20% 11% 2	456
November	1st to 10th	Day	18% 14% 29% 26% 10% 3	395
	11th to 20th	Day	22% 20% 27% 23% 7% 1	400
	21st to end	Day	23% 17% 31% 22% 7% 1	258
December	1st to 10th	Day	24% 21% 34% 14% 7%	180
	11th to 20th	Day	32% 20% 29% 15% 4	180
	21st to end	Day	24% 24% 30% 18% 3 1	198
January	1st to 10th	Night	19% 17% 37% 23% 4	760
	11th to 20th	Night	24% 16% 32% 26% 3	760
	21st to end	Night	19% 17% 36% 24% 4	836
February	1st to 10th	Night	22% 16% 36% 24% 2	760
	11th to 20th	Night	21% 19% 40% 19% 1	743
	21st to end	Night	24% 18% 34% 20% 4	628
March	1st to 10th	Night	24% 17% 32% 23% 4	760
	11th to 20th	Night	22% 21% 31% 22% 4	760
	21st to end	Night	20% 18% 33% 22% 6%	836
April	1st to 10th	Night	25% 15% 35% 21% 5%	760
	11th to 20th	Night	23% 13% 33% 25% 5%	751
	21st to end	Night	24% 14% 28% 26% 7% 1	727
May	1st to 10th	Night	27% 11% 29% 25% 7%	561
	11th to 20th	Night	21% 11% 29% 32% 6% 1	374
	21st to end	Night	15% 8% 20% 43% 14% 1	411
June	1st to 10th	Night	16% 5% 28% 36% 15% 1	380
	11th to 20th	Night	15% 6% 23% 39% 16%	380
	21st to end	Night	13% 3 22% 46% 14% 1	380
July	1st to 10th	Night	14% 3 17% 43% 21% 1	370
	11th to 20th	Night	12% 3 19% 43% 22% 1	368
	21st to end	Night	11% 5% 20% 45% 18% 1	416
August	1st to 10th	Night	13% 3 18% 44% 20% 2	459
	11th to 20th	Night	13% 3 18% 39% 24% 2	742
	21st to end	Night	15% 4 16% 37% 25% 2	836
September	1st to 10th	Night	17% 4 21% 35% 21% 2	760
	11th to 20th	Night	16% 5% 21% 32% 22% 5%	760
	21st to end	Night	19% 6% 20% 35% 17% 2	760
October	1st to 10th	Night	23% 9% 24% 25% 16% 2	760
	11th to 20th	Night	20% 10% 27% 32% 11% 1	760
	21st to end	Night	26% 10% 31% 25% 8%	836
November	1st to 10th	Night	16% 12% 32% 29% 10% 1	780
	11th to 20th	Night	23% 15% 30% 25% 7% 1	800
	21st to end	Night	20% 14% 32% 27% 7% 1	779
December	1st to 10th	Night	26% 15% 30% 24% 5%	760
	11th to 20th	Night	23% 16% 30% 27% 4	760
	21st to end	Night	26% 14% 35% 22% 3	836

Page generated at 2024-11-22 08:02:28. Version ac07

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